https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.components.forms.fieldcssclassprovider.getfieldcssclass?view=aspnetcore-6.0

The feature request is to provide a way for Telerik customers to define custom validation classes. It seems appropriate to have the FieldCssClassProvider override in Telerik components. Thus, if required customers would be able to apply custom styling and remove the default theme classes for valid and invalid state.